I didn't mean to imply that sycamore is not a good wood, structural or otherwise. My comments are strictly due to the spiral grain of the log. Sycamore logs are not all spiral grain and spiral grain occurs in many different species of wood.
I have a nice stash of quarter sawn sycamore waiting to be turned into kitchen cabinets for my house. it does move a bit but part of being a wood worker is dealing with wood movement.
I have made a piece of furniture out of spiral grained maple and thought I was planing correctly for the movement. The wood was dried properly and after 2 full years the glue joints were blown apart. If I had that stash of boards of yours I would cut it into kindleing, nice figura and all. There are enough good logs to be had that you don't need to waste time with a spiral grain log.